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Particles in the flow

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Old   May 2, 2014, 05:00
Default Particles in the flow
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Hans
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I am a student, and new to Fluent, and would really appreciate all kinds of help.
I am investigating particulate fouling of heat exchangers.
I have made simple 2-D model, that works fine in steady analysis with air.
However, I am working on injecting particles at the inlet, and hoping it is possible to make them "stick" to a geometry in the middle of the flow.
My ultimate goal is to be able to count the particles stuck to the geometry, and compare the results for different particulate sizes and masses.

I am using the Eulerian Multiphase model, and under models-discrete phases-injections, I have chosen a surface type injection at the inlet.

I have lots of questions, but to get started:
How do I make the particles that hit the geometry, the ones that are not deflected by the boundary layer, stick?
I am also having trouble visualizing the results, since the analysis is transient.

I would really appreciate all the help I could get. Thanks
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Old   May 9, 2014, 11:48
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When you set boundary conditions for the wall to be stucked on. Choose trap under dpm selection.
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Old   May 9, 2014, 14:44
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Thank you!
One more question though.

When I inject the particles, the count adds up to 300 000 particles in total every time. I understand that is some kind of limit.
I have a flowing time of 80 seconds, with particles injected from t=10s to t=70s.
The diameter range varies from 1 to 50 micron, and the mass flow is set to approximately 4 grams/minute. It should be a lot more particles.
That is no problem, the result can be scaled if Fluent handles the distribution of the particles the way I hope. The results look OK so far.

Does anyone know how Fluent selects which particles to delete, and when to inject? Does it inject all 300 000 thousand particles the first (few) time step(s), and deletes the rest? Or does it know I want to inject particles for 60 seconds, and injects 5000/s?
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Old   May 10, 2014, 06:24
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I Think you need to udf
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Old   May 19, 2014, 07:03
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Quote:
Originally Posted by nissen21 View Post
Thank you!
One more question though.

When I inject the particles, the count adds up to 300 000 particles in total every time. I understand that is some kind of limit.
I have a flowing time of 80 seconds, with particles injected from t=10s to t=70s.
The diameter range varies from 1 to 50 micron, and the mass flow is set to approximately 4 grams/minute. It should be a lot more particles.
That is no problem, the result can be scaled if Fluent handles the distribution of the particles the way I hope. The results look OK so far.

Does anyone know how Fluent selects which particles to delete, and when to inject? Does it inject all 300 000 thousand particles the first (few) time step(s), and deletes the rest? Or does it know I want to inject particles for 60 seconds, and injects 5000/s?
Hello nissen21,

I am a student as well so what I tell you right now could be wrong but it is what I understood about the surface injection.

The injection happens every injectiontimestep, you set this one in the Disperse Phase Model, so you can change the amount of particles injected with this.
And/Or
The injection type surface injects at every element 1 particle per injectiontimestep, maybe this is the limitation of your particles.
If you change the massflow it only changes the mass of the particles not the amount of them.

This is what I mean to understand during writing my thesis.

Hope its right and it helps.

Greets
Nigirim
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Old   May 21, 2014, 19:21
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Quote:
Originally Posted by nissen21 View Post
Thank you!
One more question though.

When I inject the particles, the count adds up to 300 000 particles in total every time. I understand that is some kind of limit.
I have a flowing time of 80 seconds, with particles injected from t=10s to t=70s.
The diameter range varies from 1 to 50 micron, and the mass flow is set to approximately 4 grams/minute. It should be a lot more particles.
That is no problem, the result can be scaled if Fluent handles the distribution of the particles the way I hope. The results look OK so far.

Does anyone know how Fluent selects which particles to delete, and when to inject? Does it inject all 300 000 thousand particles the first (few) time step(s), and deletes the rest? Or does it know I want to inject particles for 60 seconds, and injects 5000/s?
Unfortunately the answer to your question entirely depends upon the DPM settings. First of all, is your DPM steady or unsteady? In general, if it is steady, it will try to iterate until all the particles hit a boundary and are trapped or leave the domain or until it hits the maximum specified iterations, at which points it deletes the particles and reports them as incomplete. If you are running unsteady particle tracking, the specified number of particles will be injected at each DPM iteration and the particles already in the domain will advance the specified time step. The number of particles in the domain will increase until a steady state is achieved (i.e. number of particles leaving = number of particles injected).

As an aside, is it injecting 300k particles every DPM iteration? Based on my experience, that seems like quite a lot for a 2D simulation. FYI the number of particles is dependent upon the number of cells on your injection face, the number of bins in your PSD, and the number of turbulent tries you've specified.
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